Caption: Clinical thermometers. The mercury thermometer (top) consists of a sealed narrow-bore glass tube with a bulb at one end. It contains mercury which expands when heated and rises up the tube. The electronic thermometer (middle) uses liquid crystal technology to display the recorded temperature. The thermochromic strip (bottom) is placed against the skin and indicates temperature by changing colour at the relevant point on the strip. A clinical thermometer usually registers temperature between 35 degrees Celsius (95 degrees Fahrenheit) and 45.5 degrees Celsius (110 degrees Fahrenheit). Normal human body temperature is 36.9 degrees Celsius (98.4 Fahrenheit).